Moisture Sources of Torrential Rainfall Events in the Sichuan Basin of China During Summers of 2009–13
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1906 JOURNAL OF HYDROMETEOROLOGY VOLUME 16 Moisture Sources of Torrential Rainfall Events in the Sichuan Basin of China during Summers of 2009–13 YONGJIE HUANG Key Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS), Institute of Atmospheric Physics, Chinese Academy of Sciences, and University of Chinese Academy of Sciences, Beijing, China XIAOPENG CUI Key Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, and Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China (Manuscript received 19 November 2014, in final form 23 April 2015) ABSTRACT Water vapor sources and transport paths associated with torrential rains are very important to research and forecasts. This study investigates the main moisture sources and transport paths related to torrential rainfall events in the Sichuan basin of China, which is located east of the Tibetan Plateau, using a Lagrangian flexible particle dispersion model (FLEXPART). Based on the analysis of the torrential rainfall distribution during 2009–13, four study areas are selected in the basin. Particles that have a great contribution to the torrential rainfall events within the four study areas are traced back for 10 days, and a quantitative analysis of the contributions from various moisture sources to the torrential rainfall events is also conducted. The results indicate that a large number of target particles start at the Arabian Sea and the Bay of Bengal, land on the Indo-China Peninsula, and finally reach the study areas. This is an important moisture transport path for the torrential rainfall events within the four study areas. Another important path is from the neighborhood of the Sichuan basin. The total moisture supplies from all examined moisture sources within the whole atmo- spheric layer account for more than 90% of precipitation within the study areas. There are two major moisture sources, the Sichuan basin and the Bay of Bengal, and the South China Sea could be another important moisture source region for the torrential rains in the northeastern Sichuan basin. 1. Introduction Richter scale) and the Ya’an earthquake in 2013 (7.0 on the Richter scale). Torrential rains, which can cause floods, landslides, Precipitation occurs throughout the year in the Sichuan debris flows, and other geological hazards resulting in basin, mainly as a result of the East Asian monsoon, the severe loss of life and property damage, are a great Indian monsoon, and the atmospheric circulation system challenge to weather forecasters. Serious floods, land- interacting with the Tibetan Plateau. Torrential rainfall in slides, and debris flows often occur in the Sichuan basin the Sichuan basin usually occurs in the summer season, of China, which is located east of the Tibetan Plateau, June–September. Figure 1 shows the topographic height south of the Qinling Heights, and north of the Yunnan– in Sichuan and distribution of total torrential rainfall (24-h Guizhou Plateau, especially after violent earthquakes, accumulated precipitation $50 mm, based on the pre- like the Wenchuan earthquake in 2008 (8.0 on the cipitation grading standards used at the National Mete- orological Center, China) in the Sichuan region from June to September 2009–13. The terrain at the edge of the Corresponding author address: Dr. Xiaopeng Cui, Key Labora- Sichuan basin is very complex, especially on the western tory of Cloud-Precipitation Physics and Severe Storms (LACS), side of the basin, adjacent to the Tibetan Plateau, where Institute of Atmospheric Physics, Chinese Academy of Sciences, No. 40, Huayanli, Deshengmenwai, Chaoyang District, Beijing the terrain slope is particularly steep (Fig. 1a). Heavy 100029, China. rainfall mainly occurs in the Sichuan basin, especially at E-mail: [email protected] the edge of the basin, where terrain is complex and steep DOI: 10.1175/JHM-D-14-0220.1 Ó 2015 American Meteorological Society Unauthenticated | Downloaded 10/05/21 03:19 PM UTC AUGUST 2015 HUANG AND CUI 1907 FIG. 1. (a) Topographic height (m) and (b) distribution (mm) of total torrential rainfall (24-h accumulated precipitation $50 mm) during June–September 2009–13 in Sichuan. Red rectangles represent the Sichuan basin. with four strong centers (Fig. 1b), implying complex in- There are several methods to identify moisture teractions between circulation and topography. The first sources and transport paths for rainfall events, such as center is located in the Ya’an area near steep terrain east isotopic analysis (Weyhenmeyer et al. 2002; Bonne et al. of the Tibetan Plateau. The second one is situated in the 2014), Eulerian methods (Holman and Vavrus 2012; Sun northeastern corner of the basin, the Daba Shan zone. and Wang 2013), and Lagrangian methods (Gustafsson The third one is in the northwestern part of the basin, and et al. 2010; Drumond et al. 2011a,b). However, it is im- the last one is in the central region of the basin. The possible for isotopic analysis methods to examine past terrains of three of these regions—the Ya’an region, the events for which no rain samples are available northeastern basin, and the northwestern basin—are very (Gustafsson et al. 2010). For the moisture flux, the con- complicated, which may be closely related with the oc- ventional Eulerian method can only give simple water currence of heavy rainfall in these regions (Fig. 1b). vapor transport paths and fails to accurately identify For torrential rainfall events to occur, moisture the moisture source regions that contribute to torren- sources (suitable regions of evaporation), transport paths, tial rainfall events (Sodemann et al. 2008). Recently, a and uplifting motions are three indispensable conditions sophisticated Lagrangian flexible particle dispersion (Gustafsson et al. 2010). It is crucial to study moisture model (FLEXPART) was developed and widely used source regions and transport paths for heavy rainfall to study moisture sources and transport paths (e.g., (Newell et al. 1992). In general, local evaporation from Stohl and James 2004, 2005; Stohl et al. 2008; Sodemann the surface of the region, moisture already present in the and Stohl 2009; Gimeno et al. 2010a,b, 2013; Chen et al. atmosphere over the region, and water vapor trans- 2013; Gómez-Hernández et al. 2013). ported into the region by wind have been identified as Huang and Cui (2015) used FLEXPART to study the possible moisture sources for precipitation (Brubaker moisture sources of an extreme precipitation event that et al. 1993). Gustafsson et al. (2010) found that atmo- occurred in Sichuan in July 2013, causing substantial spheric transport is a prerequisite for extreme rainfall losses. They found that water vapor originating from events to occur in southern Sweden, and regional the Indian Peninsula–Bay of Bengal–Indo-China Pen- moisture may also play a key role. Drumond et al. insula region had the highest contribution to this (2011a) found that the Arabian Sea and the Bay of extreme event. However, there was only one case Bengal are important moisture sources for the southern analyzed in their study, and a composite analysis of and central regions of China by using a Lagrangian ap- multiple cases in the Sichuan basin of China should be proach. As for the Sichuan basin with its very complex conducted to make their conclusions more statistically terrain, what the most important moisture sources and significant (Huang and Cui 2015). In this study, by using transport paths are for the torrential rainfall events the same Lagrangian method, the moisture transport within the basin is still a big question to be solved, one paths and main moisture source regions for the multi- that is crucial to the research and forecasting of tor- ple torrential rainfall events in the Sichuan basin of rential rains, related floods, and geological hazards. China are studied. Meanwhile, we also quantitatively Unauthenticated | Downloaded 10/05/21 03:19 PM UTC 1908 JOURNAL OF HYDROMETEOROLOGY VOLUME 16 estimate contributions from various moisture sources to the heavy rainfall events. 2. Data, model, and methodology The precipitation data used in this study are from a 0.1830.18 resolution dataset from 2009 to 2013 gener- ated through hourly precipitation observations by au- tomatic weather stations in China and merged with CPC morphing technique (CMORPH) satellite data (Pan et al. 2012; Shen et al. 2013). The topographic height data shown in Fig. 1a are from the Global Land One-km Base Elevation Project (GLOBE) database (www.ngdc. noaa.gov/mgg/topo/globe.html). a. Study areas and selection of torrential rainfall events FIG. 2. PDF (%; gray line) and CDF (%; black line) of the For the selection of the regions of interest (study total torrential rainfall during June–September 2009–13 in the areas), probability density function (PDF) and cumula- Sichuan basin (red rectangles in Fig. 1). The horizontal and vertical dashed lines denote 85% CDF and 1300 mm torrential rainfall, tive distribution function (CDF) curves of the heavy respectively. rainfall in the Sichuan basin (28.58–33.08N, 102.08– 108.68E; red rectangles in Fig. 1) were plotted and are shown in Fig. 2. From Fig. 2, it is found that inflection with a 18318 resolution on 26 vertical levels (http://rda. points appear around 1300 mm on the curves corre- ucar.edu/datasets/ds083.2/) for the region 108S–608N, sponding to 85% CDF. Based on analysis of this 408–1608E, and the period from 2009 to 2013, using the threshold value of the total torrential rainfall in the Si- domain filling mode, with a total of 1.2 million particles chuan basin, four study areas are selected in the Sichuan released. The model outputs are recorded every 3 h and basin, as shown in Fig. 3 (middle) and marked by rect- include the identity number of particles, the three- angles.